Light-Emitting Cells Ramp up Solar Efficiency

Like all renewables, photovoltaics (PVs) are in a constant state of innovation. Researchers are forever striving for breakthroughs in materials and productivity to help them lower costs and chip away at the historical advantage enjoyed by fossil fuels in mainstream energy markets.

Recently, scientists at the University of California, Berkeley, achieved a breakthrough in PV efficiency that is not only compelling but somewhat counterintuitive. They discuss their findings in a paper prepared for the May 2012 Conference on Lasers and Electro-Optics in San Jose, Calif.

In the paper, they claim to have found a way to dramatically increase the efficiency of electricity captured by solar cells by allowing the cells to generate their own light in addition to the sunlight they absorb.

The scientists captured a thermodynamic link between absorbing light and emitting it. More specifically, the cells were designed to integrate a process known as electroluminescence, in which free-roaming electrons generate their own light, the same process that is at work in a light-emitting diode (LED).

In a typical PV cell, the electrons are first knocked free in the semiconductor material by the photons that are absorbed from sunlight. These electrons are captured to form an electrical current, but the process of knocking them free also generates additional photons. These photons are usually lost or absorbed by the cell internally, but the Berkeley scientists designed their cells to allow this naturally occurring light to be released. By releasing the photons, they found that the cells also generated more electricity.

The cell the scientists created using this process reached an efficiency level of 28.3 percent, breaking the old record of 26 percent set last year. They see this as a major step toward achieving the maximum theoretical efficiency of solar cells, which is 33.5 percent. On average, most solar cells convert less than 20 percent of the sunlight they absorb into electricity.